The present invention relates to utilizing and/or controlling a plurality of magnetrons that are powered by a single power supply.
Microwave heating is a technique that can be applied with great advantage in a multiple of processes which include the supply of thermal energy. One advantage is that the heating power can be controlled in the absence of any inertia.
One drawback, however, is that microwave equipment is often more expensive than conventional alternatives. A magnetron of such heating equipment may be driven by a power unit with associated control system, which constitute the major cost of the equipment. Since the output power of the magnetron is limited, heating equipment may require the presence of a significant number of magnetrons and associated power units and control systems to achieve a given heating requirement.
Magnetrons may be used to generate radio frequency (RF) energy. This RF energy may be used for different purposes such as heating items (i.e., microwave heating) or it may be used to generate a plasma. The plasma, in turn, may be used in many different processes, such as thin film deposition, diamond deposition and semiconductor fabrication processes. The RF energy may also be used to create a plasma inside a quartz envelope that generates UV (or visible) light. Those properties decisive in this regard are the high efficiency achieved in converting d.c. power to RF energy and the geometry of the magnetron. One drawback is that the voltage required to produce a given power output varies from magnetron to magnetron. This voltage may be determined predominantly by the internal geometry of the magnetron and the magnetic field strength in the cavity.
Some applications may require two or more magnetrons to provide the required RF energy. In these situations, an individual power source has been required for each magnetron. Two or more magnetrons may be coupled to a power supply in parallel. However, two magnetrons of identical design may not have identical voltage versus current characteristics. Normal manufacturing tolerance and temperature differences between two identical magnetrons may yield different voltage versus current characteristics. As such, each magnetron may have a slightly different voltage. For example, the magnetrons may have mutually different operating curves such that one magnetron may produce a higher power output than the other magnetron. The magnetron having the higher output power may become hotter than the other, wherewith the operating curve falls and the power supply will be clamped or limited to a lower output voltage. This may cause the power output of the magnetron producing the higher output to fall further until only one magnetron produces all the power due to the failure to reach the knee voltage of the other magnetron. It is desirable to utilize a plurality of magnetrons without these problems.
Embodiments of the present invention may provide a system that includes a power supply device to supply a current, at least three magnetron devices to be powered by the power supply device, and a control circuit to apportion an amount of current to each of the plurality of magnetron devices.
The control circuit may include a first hall effect sensor coupled between the power supply device and a first one of the magnetron devices, a second hall effect sensor coupled between the power supply device and a second one of the magnetron devices, and a third hall effect sensor coupled between the power supply device and a third one of the magnetron devices.
The third magnetron device may be a master magnetron device, the second magnetron device may be a slave magnetron device, and the third magnetron device may be a slave magnetron device.
The first hall effect sensor may sense current in the first magnetron device, the second hall effect sensor may sense current in the second magnetron device, and the third hall effect sensor may sense current in the third magnetron device. The control circuit may further include a first compare device to compare an output of the first hall effect sensor and an output of the second hall effect sensor. The control circuit may further include a second compare device to compare an output of said first hall effect sensor and an output of said third hall effect sensor.
Embodiments of the present invention may further include a system that includes a power supply device, a first magnetron device and a second magnetron device each to be powered by the power supply device. A first sensor device may sense current through the first magnetron device and a second sensor device may sense current through the second magnetron device. A first compare device may compare an output of the first sensor device and an output of the second sensor device. A first mechanism may adjust current to the second magnetron device based on the comparison of the first compare device. The system may further include a third magnetron device to be powered by the power supply device, a third sensor device to sense current through the third magnetron device. A second compare device may compare an output of the first sensor device and an output of the third sensor device. A second mechanism may adjust current to the third magnetron device based on the comparison of the second compare device.
Embodiments of the present invention may further provide a method of powering at least three magnetrons. The method may include providing a first current along a first signal line to a first magnetron device, providing a second current along a second signal line to a second magnetron device, and providing a third current along a third signal line to a third magnetron device. Current may be apportioned to each of the first, second and third magnetron devices.
Other objects, advantages and salient features of the invention will become apparent from the detailed description taken in conjunction with the annexed drawings, which disclose preferred embodiments of the invention.